Degenerate Electron-hole Plasma Research Articles

The electric field of an electron in an electron–hole plasma with degenerate electrons: Possibility of formation of a superconductivity state

We consider the possibility of the formation of a superconductivity state either in a semiconductor or in an electron–hole plasma with degenerate electrons due to the attractive forces between the electrons as a result of the exchange effects through the electron–hole sound wave by an analogy to the phonon waves in a solid state. We have determined an interaction potential between two electrons in a degenerate electron–hole plasma. The potential appears to be attractive at distances much larger than the Debye radius and decreases as 1/r3. We discuss the conditions in which the bound electron state, the so‐called “Cooper Pair,” in a such field can be formed.

Features of the transformation of the exciton cathodoluminescence spectra of CdSe epitaxial layers with increasing excitation level

Features of the transformation of the cathodoluminescence spectra of CdSe epitaxial layers with increasing excitation level are studied. It is shown that the spectra at 78 K exhibit the following transformation as the excitation-current density increases: (A-exciton line)-(non-degenerate electron-hole plasma bands)-(degenerate electron-hole plasma bands).

Terahertz lasers based on optically pumped multiple graphene structures with slot-line and dielectric waveguides

Terahertz (THz) lasers on optically pumped multiple-graphene-layer (MGL) structures as their active region are proposed and evaluated. The developed device model accounts for the interband and intraband transitions in the degenerate electron-hole plasma generated by optical radiation in the MGL structure and the losses in the slot or dielectric waveguide. The THz laser gain and the conditions of THz lasing are found. It is shown that the lasers under consideration can operate at frequencies ≳1 THz at room temperatures.

Temporal Behavior of the Energy Relaxation of Hot Carriers in ZnO Single Crystals

Energy relaxation of optically-generated hot carriers in ZnO is explored theoretically as a function of time. Cooling curves are extracted from the energy loss rates obtained by using the Kogan formula extended to a degenerate electron-hole hot plasma at low lattice temperatures. The energy losses of the carriers by various carrier-phonon interactions are taken into account. The screening of the carrier-phonon interactions is included within the random phase approximation. We observed an initial slow energy relaxation process followed by a rapid relaxation at both high and low carrier temperatures. The dominant relaxation process at the earlier cooling stage in the temperature range 10 2 K Tc 10 3 K is the excitations of optical phonons. The energy relaxation in the low carrier temperature range (Tc 10 2 K) is determined mainly by acoustic phonon scattering. The initial relaxation time of ZnO is found to be on the order of femtoseconds. The relaxation time is increased by a factor of ten if carrier screening eects are taken into account, irrespective of the initial carrier temperature.

Super band-gap time-resolved luminescence study of degenerate electron–hole plasma in thin GaAs epilayers

Super band-gap time-resolved photoluminescence is employed to measure the transport properties of degenerate electron–hole gas in thin GaAs epilayers. It is found that the luminescence decay at wavelengths shorter then the energy gap wavelength is much faster then expected from a simple diffusion–reabsorption model. The results are explained by using a transport model based on Fermi–Dirac carrier statistics and nonparabolic band structure. We have found that only by introducing the above two phenomena the photoluminescence spectra at all energies can be fitted. The importance of the results in studies of hot carrier energy loss rates is discussed.

The effects of carrier transport on the photoluminescence of degenerate electron-hole plasma in GaAs epilayers

Time resolved photoluminescence (TRPL) is employed to study photogenerated electron-hole plasma expansion under strong illumination conditions in thin GaAs epilayer. We have observed spectral dependencies similar to ones which are usually observed on carrier's cooling. However, in our case they are caused by the diffusion of the degenerate electron-hole plasma perpendicular to the crystal surface. We have studied the influence of the degenerated carrier transport on the luminescence characteristics of bulk samples, both experimentally and by simulations. We suggest using this method to measure the transport coefficients of both degenerate and hot excess carriers in semiconductor structures.

Monte-Carlo Simulations of the Coulomb Boltzmann Kinetics in a Quasi-Two-Dimensional Electron–Hole Plasma for Various Screening Models

For carrier-carrier scattering the relaxation kinetics of a quasi-two-dimensional degenerate electron-hole plasma is studied in the framework of the Boltzmann equation using both a static and a dynamic RPA screening. The time development of an initial nonequilibrium distribution is calculated by ensemble Monte-Carlo simulation. A comparison of the results for both screening models for the energy relaxation and the total scattering rate yields conditions for the validity of static screening.

Photoconductivity of a degenerate electron-hole plasma in GaInAs/AlInAs MQW structures

Degenerate electron-hole plasmas have been produced in the quantum wells of GaInAs/AlInAs MQW systems using 100 ps pulses from a Q-switched, mode-locked Nd-YAG laser. Photoconductivity parallel to the layers showed band-filling effects, and good exponential decays were observed over several orders of magnitude of carrier density. For a 50 well system with 50 AA wells and 100 AA barriers the recombination time constant was 3.6+or-0.2 ns between 300 K and 150 K, rising to 7 ns at 40 K. There was no indication of Auger processes, implying that the Auger coefficient was less than 10-30 cm6 s-1, which is much smaller than the reported values. The intensity of light at the onset of band filling reduced linearly with reducing temperature between 300 K and 150 K following a trend expected from the temperature dependence of the band gap. The initial well photoconductivity produced by a given light intensity reduced with reducing temperature. The electron mobility in the electron-hole plasma was about 400 cm2 V-1 s-1. No change with carrier density was observed. Below 40 K short time constant components tend to dominate the decay and the photoconductivity becomes noisy. In the case of a 20 well sample the signal was heavily influenced by photoconductivity in the semi-insulating InP substrate. It is pointed out that band filling allows a distinction to be made between well and substrate/cladding photoconductivities.

Coupling of plasmons to polar phonons in GaAs quantum wells.

Mode coupling between the degenerate electron-hole plasma and longitudinal-optical phonons in GaAs quantum wells is treated theoretically. Both the plasmons and coupled modes are found to be confined in long-wavelength ranges. In contrast to bulk crystals, the condition that the dielectric function of the coupled system is negative is necessary. The wave numbers of the coupled modes in the GaAs well of 50 A\r{} in width are smaller than 2\ifmmode\times\else\texttimes\fi{}${10}^{6}$ and 1.5\ifmmode\times\else\texttimes\fi{}${10}^{6}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ at the electron density of 1\ifmmode\times\else\texttimes\fi{}${10}^{17}$ and 1\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$, respectively, where the modes exhibit no Landau damping. These results indicate that the plasma does not affect carrier heating through the Fr\ohlich interaction.

Direct auger recombination in degenerate direct gap semiconductors

We show that the density dependence of the Auger lifetime strongly differs from the usual Cn −2 law in the case of a direct process (without phonons) taking place in a degenerate electron-hole plasma with one parabolic conduction band and one parabolic valence band: the lifetime roughly increases by a factor 20 when the plasma Fermi energy E F∼n 2 3 goes from the band gap E G to the threshold E 0 ( ∼E G 6 ) of this direct process, while, close to threshold, it behaves like ( E F − E 0) −4.

Injection of degenerate electron-hole plasma

Injection of degenerate electron-hole plasma

Helical density waves in a strongly degenerate electron-hole plasma

Helical density waves in a strongly degenerate electron-hole plasma

Spectral and temporal characteristics of emission from degenerate electron–hole plasma in GaAs and CdS at 300°K

Investigations were made of the spectral and temporal characteristics of spontaneous and stimulated emission from a degenerate electron-hole plasma in GaAs and CdS excited by an electron beam having an energy of 150 keV and a pulse current of up to 650 A. The measurements were made at 300°K with a temporal resolution of ~10–11 sec. A study was made of the evolution kinetics of the radiation spectra as a function of the excitation rate. Determinations were made of the critical carrier densities at which the bound states were destroyed as a result of screening of the Coulomb interaction and the spectra became distorted: the narrow lines corresponding to carrier recombination via bound states disappeared and emission from the electron-hole plasma was observed. The carrier recombination times in the plasma were (0.3±0.1)×10–9 sec in GaAs and (1.4±0.3)×10–9 sec in CdS. The position on the energy scale and the shift of the plasma radiation spectra with increasing excitation level agreed with the theoretical concepts.

Mechanism of stimulated emission from laser screens made of II-VI semiconductor compounds

The characteristics of laser screens made of II-VI semiconductor compounds (and designed to operate in electron-beam tubes) were investigated in the range 80–300°K. The spectral characteristics of spontaneous and stimulated emission and the threshold parameters were determined. It was concluded from these data that, in the temperature range, 80–300°K the laser action in these screens occurred as a result of radiative recombination in a degenerate electron-hole plasma.

The pinch effect in a solid-state plasma

This article reviews the experimental and theoretical studies of the pinch effect in a solid-state plasma in the period 1958-1975. Different methods of observing the pinch effect and ways of initiating and suppressing this effect are described. Special attention is paid to the time evolution of this phenomenon. The fundamental features of the pinch effect in semiconductors under lattice-heating conditions are pointed out. The problems are discussed in detail of plasma stability in the pinch effect, as well as the mechanisms of breakdown of a pinch in a longitudinal magnetic field. The form of the recombination-radiation spectra in the pinch effect in a degenerate electron-hole plasma is analyzed. The fundamental experimental results from studying a θ-pinch in InSb and Ge are given and analyzed. The applied aspects of studying the pinch effect in a solid-state plasma are pointed out, and unsolved problems are noted. Analogies are pointed out in a number of cases with the corresponding gas-discharge developments.

Electron–Hole Liquid above the Critical Point

AbstractAt sufficiently high pumping levels, carrier densities of more than 2 × 1017 cm−3 can be produced in doped Ge or small crystals of intrinsic Ge. As a result, the crystal can be entirely filled with a degenerate electron–hole plasma. With increasing temperature this system does not undergo a phase transition to a low density free exciton gas, even at temperatures above the critical point.

Self-focusing of electromagnetic waves in a degenerate electron-hole plasma

The free carrier nonlinear dielectric constant of a degenerate electron-hole plasma (e.g., Ge) in the presence of a Gaussian electromagnetic beam has been studied by a kinetic treatment. The redistribution of carriers (electrons and holes) is the source of nonlinearity and is effective in causing the self-focusing of the beam. The rise in carrier temperature due to the wave field is almost unaffected by the degeneracy, whereas the nonlinearity is considerably affected by it. The increase of degeneracy (by increasing the equilibrium carrier concentration at the fixed lattice temperature) increases the nonlinear dielectric constant. Hence self-focusing is enhanced by degeneracy.